液压油污染度等级 ISO and NAS GB 02-10-07

Particle contamination in oil is specified from particle count. Two basic standards the ISO and NAS systems are commonly used as contamination reference. The two cleanliness stan-dards can not be directly compared or converted, as the basic principles within the two systems differ to much. This is explained in the next pages.

However, the following tables gives some rough guidelines of common practice for setting targets of cleanliness levels in dif-ferent systems. As seen both ISO 4406 and NAS 1638 are repre-sented. These guidelines are minimum fluid cleanliness levels required for an acceptable lifetime of equipment and compo-nents.

Many factors influence lifetime and demands to fluid quality. High reliability systems enhance demands to quality, and high pressure systems and heavy bearing load increase demands. The last three columns of the tables indicate the range of the GreenOil filter system. Although the filters may be put into ser-vice in many application, parameters as fluid volume and vis-cosity should be taken into consideration before expectations to contamination limits are set.

Hydraulic Equipment and Components Pressure Range GreenOil Filter Inserts

ISO 4406 NAS 1638

H

T M Silt sensitive, aerospace, robots, High pressure 250-400 bar

14/12/9 4 ISO 10/6 NAS 3

Servo systems, injection moulding, High pressure 250-400 bar 16/14/11 5

Proportional and flow valves, High pressure 250-400 bar 17/15/12 6

Piston pumps and motors, Normal pressure 150-250 bar 18/16/13 7

Typical new hydraulic oil

18/16/13 7

Gear pump and motors, Medium pressure 50-150 bar 19/17/14 8

Cylinders and Flow Control Low pressure 0-50 bar 20/18/15

9

Lubrication Oil

Equipment and Components

Ball bearings, turbine oils,

Small and medium gearboxes 14/12/9 4

Roller bearings

Transmission gearboxes 16/14/11

5

ISO 14/11 NAS 5 Journal bearings Industrial gearboxes

17/15/12 6

Mobile equipment and gearboxes Paper mill

18/16/13

7

ISO 16/12 NAS 7

Diesel engine lubrication

19/17/14 8

Heavy duty gearboxes

20/18/15

9

Typical new lubrication oil

20/18/15 9

Typical in-line filtration

21/19/15

10

Minimum

Class Requirement Page 1 of 3

Introduction

Contamination in oil is specified from particle count. Two basic

methods are used:

Laser based particle count analysis equipment gives directly

information on particle sizes (micron= u) and figures within

specified size ranges.

The other method utilize filtering an oil sample through an very

fine mesh filter paper. The particles on the surface of the filter

paper is then monitored in a microscope and compared to

standard contamination pictures to indicate the degree of con-

tamination.

Contamination classes

Instead of specifying particle counts contamination is sepa-

rated into classes defined in two major systems ISO

(International Standard Organisation) and NAS (National Air-

space Standard). Each class defines a range of counts within

an exponential scale.

Unfortunately, the two systems are not identical and can not be

converted in simple mathematics. However, some simple

guidelines can be given. First of all let’s look at the two systems.

NAS1638

The NAS system divides particles in 5 ranges.

Furthermore, the NAS system specify different counts within

each particle range to score a specific class.

In practice oil samples will show up to gain almost same NAS

class rating within the different particle ranges. The system is

designed to match the most common found contamination

which has really many small particles and fever big particles.

The sidebar example shows a typical oil analysis with counts

divided in the 5 classes. As seen the classes ranges from 3 to 6,

however, the resulting NAS class is defined as the particle count

with the highest (worse) score, and only this class is specified.

The sidebar example will be classified as “NAS1638 class 6”.

Classes

u 5 to 15 15 to 25 25 to 50 50 to 100 > 100

00 125 22 4 1 0

0 250 44 8 2 0

1 500 89 16 3 1

2 1.000 178

32 6 1

3 2.000 356 63 11 2

4 4.000 712

126

22 4

5 8.000 1.425 253 45 8

6 16.000 2.850

506

90 16

7 32.000 5.700 1.012 180 32

8 64.000

11.400

2.025

360

64

9 128.000 22.800 4.050 720 128

10 256.000 45.600

8.100

1.440

256

11 512.000 91.200 16.200 2.880 512

12 1.024.000

182.400

32.400

5.760

1024

Particle Classes Size Range per 100 ml

NAS 1638

Particle range Counts Class

5-15 u 8450 6

15-25 u 11982 5

25-50 u 312 6

50-100 u 46 6

>100 u 2 3

Resulting Class 6

NAS analysis example